Color electrophoresis type display medium panel

ABSTRACT

One embodiment of the present invention is a color electrophoresis type display medium panel having a transparent substrate, a color filter layer, a transparent electrode layer, a microcapsule layer, an adhesive layer and a rear electrode plate, wherein the microcapsule particle has a specific distribution wherein an average particle diameter of the microcapsule in a direction observed from a viewer is defined as X, and an average particle diameter of the microcapsule in another direction perpendicular to the direction observed from a viewer is defined as Y.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a microcapsule type electrophoresisdisplay panel with a color filter. The panel has a structure in which amicrocapsule layer is arranged between a pair of electrode plates facingeach other, one of the electrode plates having a color filter layer, andan electrophoresis ink being enclosed in a microcapsule. The panel canhave an improved image quality.

2. Description of the Related Art

In recent years, due to the development of information devices, variousinformation displays are also being developed. A CRT or a liquid crystalusing a backlight are main stream display panels of variableinformation. However, when a light emitting type display such as a CRTor a liquid crystal display using a backlight is watched for a longtime, the human eye becomes strained. Therefore, such a display is notsuitable for reading a document or the like for a long time.

In addition, a screen in a liquid crystal display without a backlightbecomes very dark due to the use of a polarizing plate which reducesvisibility. Further, a display image of these displays does not havememory characteristics. If an electric energy supply is stopped, adisplay image suddenly disappears. Therefore, a display which does notcause eye strain, has excellent visibility, low power consumption, andimages having memory characteristics, is required.

As a reflection type display device which rarely causes eye strain, forexample, an electrophoresis type display panel is proposed as shown inpatent document 1, the electrophoresis display panel having a pair ofmutually facing electrodes and an electrophoresis display layer arrangedbetween the electrodes. This electrophoresis type display panel displaysa character or an image by reflection light. This principle is the sameas in printed paper. Therefore, the display panel rarely causes eyestrain and is suitable for viewing for long periods.

The principle of this electrophoresis display panel is as follows. Avoltage is applied to a dispersion liquid in which an electricallycharged particle is dispersed. Thereby, the charged particle moves, andimage display becomes possible. A microcapsule type electrophoresisdisplay panel in which a colored charged particle is enclosed in amicrocapsule and the microcapsule is arranged between a pair of mutuallyfacing electrodes has advantages such as low driving voltage and highflexibility and is being used practically and continuously developed.

This electrophoresis panel is suitable as a substitute for a display ofan information portable device such as a PDA (personal digitalassistance) or an electronic book which are predicted to be used widely,or a printed matter such as a newspaper, a book, a magazine and aposter, or displaying a hard copy on paper from a printer. Theelectrophoresis panel generally has a structure of two color displays(white and black display). However, in recent years, multi-colorcolorization is required for the purpose of displaying the magazine or acolor printed matter.

In order to realize a multi-color colorization of the electrophoresispanel, the following ideas are disclosed. For example, using anelectrophoresis particle of multi-color equal to or more than twocolors, the particle is arranged in a predetermined pixel by patterningusing photolithography (patent document 2) or by photolithograph andink-jet (patent document 3). In addition, in patent document 4, a cellframe for receiving a microcapsule is formed in advance, and a pluralityof microcapsules are arranged in a desirable position, thereby displayof a plurality of colors becomes possible. However, arrangingmulti-color microcapsules at a predetermined pixel requires moreprocesses and is complex. Therefore, there are actually manytechnological difficulties.

Therefore, in patent document 5, a color filter substrate is attached toa white and black electrophoresis display panel. Thereby, it is possibleto display multi colors without accurate position adjustment between amicrocapsule and a pixel. However, in this method, because a separatelymanufactured color filter is attached on a white and black reflectiontype electrophoresis display panel, it is necessary to arrange anadhesive for the attachment. Therefore, display brightness is low andattachment of a color filter is difficult which reduces productivity.Further, because the distance between a color filter layer and anelectrophoresis display layer is large, there is a disparity in colordepending on the viewing angle. An advantage of electronic paper whichis not influenced by the viewing angle disappears.

Then, the inventors of the present invention found that, in the casewhere a microcapsule ink is directly formed on a transparent electrodelayer of a color filter, display brightness and viewing angle can beimproved. However, as mentioned above, this electrophoresis displaypanel displays a character or an image by a reflected light. Lightpasses twice through a colored layer of a color filter. Therefore, it isnecessary to raise reflectance. That is, it is important to increase theratio of a microcapsule which contributes to display in a microcapsulelayer.

-   Patent document 1: JP-B-S50-015115-   Patent document 2: JP-A-2002-365668-   Patent document 3: JP-A-2003-156770-   Patent document 4: JP-A-2003-295234-   Patent document 5: JP-A-2003-161964

The present invention was made by considering the above background. Theobject of the present invention is to provide a multi color displaymicrocapsule type electrophoresis type display medium panel withexcellent uniform display quality in which a reduction of displaybrightness and narrowing of viewing angle are resolved.

SUMMARY OF THE INVENTION

The inventors of the present invention studied the above problem,thereby the inventors found the following facts and the presentinvention was made. In the case where a microcapsule ink is directlyapplied to a transparent electrode layer on a color filter layerarranged on a transparent substrate in a viewer side, display brightnessand viewing angle are improved. Further, in the case where distributionof a particle diameter of a microcapsule in a microcapsule layer isadjusted to be within a constant range, reflectance of white is high andnon-uniformity of density is small. Thereby a multi color display panelwhich can improve image quality is obtained.

That is, a first aspect of the present invention is A colorelectrophoresis type display medium panel having a transparentsubstrate, a color filter layer, a transparent electrode layer, amicrocapsule layer, an adhesive layer and a rear electrode plate,wherein the transparent substrate, the color filter layer, thetransparent electrode layer, the microcapsule layer, the adhesive layerand the rear electrode plate are arranged in that order, wherein themicrocapsule layer is directly formed on the transparent electrodelayer, the microcapsule layer is comprised of a binder resin and amicrocapsule, the microcapsule being dispersed in the binder resin, adispersion liquid in which electrophoresis particles are dispersed in atransparent dispersion medium is enclosed in the microcapsule, and anoptical reflection property of the microcapsule changes by a change ofan electric field by an applied voltage, the rear electrode plate is anelectrode plate in which a pixel electrode is arranged on a substrate,and the microcapsule has a following distribution; an average particlediameter of the microcapsule in a direction observed from a viewer isdefined as X, and an average particle diameter of the microcapsule inanother direction perpendicular to the direction observed from a vieweris defined as Y, X=35-45 μm, a proportion of the microcapsules when aparticle diameter of the microcapsule is equal to or more than X1 (=X−20μm) and a particle diameter of the microcapsule is equal to or less thanX2 (=X+20 μm), is equal to or more than 80%, a proportion of themicrocapsules when a particle diameter of the microcapsule is less thanX1, is less than 20%, a proportion of the microcapsules when a particlediameter of the microcapsule is more than X2, is less than 5%, and,Y=35-45 μm, a proportion of the microcapsules when a particle diameterof the microcapsule is equal to or more than Y1 (=Y−20 μm) and aparticle diameter of the microcapsule is equal to or less than Y2 (=Y+20μm), is equal to or more than 80%, a proportion of the microcapsuleswhen a particle diameter of the microcapsule is less than Y1, is lessthan 20%, and a proportion of the microcapsules when a particle diameterof the microcapsule is more than Y2, is less than 5%.

In addition, a second aspect of the present invention is the colorelectrophoresis type display medium panel according to the first aspect,wherein the electrophoresis particles are two kinds of particles havingdifferent surface electrical charges, one of the particles being acolored particle and the other being a white particle.

In addition, a third aspect of the present invention is the colorelectrophoresis type display medium panel according to the first aspect,wherein a film thickness of the color filter layer is 0.5-2.0 μm,wherein a step between pixels or inside a pixel inside a display screen,the step being the difference of the film thickness, is equal to or lessthan 0.3 μm, one of the pixels does not overlap with an adjacent pixel,and a top edge of each of the pixels of a trapezoid shape is within 5.0μm from a border of the pixel.

Next, a fourth aspect of the present invention is the colorelectrophoresis type display medium panel according to the first aspect,wherein, in a state where the microcapsule layer is observed from adirection of a cross section of the panel, a thickness of themicrocapsule layer is equal to or less than X or Y, and is equal to ormore than 0.8×X1 or 0.8×Y1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional diagram explaining a structurerelated to one embodiment of a color electrophoresis type display mediumpanel of the present invention.

FIG. 2 is a schematic enlarged cross sectional diagram explaining astructure related to one embodiment of a color electrophoresis typedisplay medium panel of the present invention.

FIG. 3( a) is a diagram explaining a definition (X and Y) related to aparticle diameter of a microcapsule used in the present invention.

FIG. 3( b) is a diagram explaining a distribution of a particle diameterof a microcapsule in a microcapsule layer related to the presentinvention.

FIG. 4 is a schematic enlarged cross sectional diagram of one example ofa color filter comprising a color electrophoresis type display mediumpanel of the present invention.

FIG. 5( a) is an enlarged planar view explaining one example of a colorfilter comprising a color electrophoresis type display medium panel ofthe present invention.

FIG. 5( b) is a planar view explaining one example of a color filtercomprising a color electrophoresis type display medium panel of thepresent invention.

-   1 . . . a transparent substrate; 2 (RGB) . . . a color filter layer;    4 . . . a transparent electrode layer; 5 . . . a microcapsule; 6 . .    . a colored particle; 7 . . . a white particle; 8 . . . a    transparent dispersion medium; 9 . . . a microcapsule shell; 10 . .    . a microcapsule layer; 11 . . . a binder resin; 16 . . . an    adhesive layer; 30 . . . a pixel electrode; 40 . . . a rear    electrode plate; 50 . . . a rear substrate.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a color electrophoresis type display medium panel of thepresent invention is explained in detail based on an embodiment.

FIG. 1 is a schematic cross sectional diagram explaining a structureexample of a color electrophoresis type display medium panel related toone embodiment of the present invention. FIG. 2 is an enlarged diagramof FIG. 1. As shown in FIGS. 1 and 2, a color electrophoresis typedisplay medium panel of the present invention is a display panel havinga transparent substrate (1), a color filter layer (2), a transparentelectrode layer (4), a microcapsule layer (10), an adhesive layer (16)and a rear electrode layer which are arranged in that order. Amicrocapsule layer is directly formed on a transparent electrode layer(4). A microcapsule layer is comprised from a microcapsule (5) dispersedin a binder resin (11). In the microcapsule (5), a dispersion liquid inwhich an electrophoresis particle of a colored particle (6) and a whiteparticle (7) is dispersed in a transparent dispersion medium (8) isenclosed. If an electric field is changed by applying a voltage, anoptical reflectance property of the microcapsule changes. A rearelectrode plate (40) is a rear substrate (50) with a pixel electrode(30).

In addition, (not shown in figures) according to necessity, in order toreduce bumps of a microcapsule (5), a surface flattening layer (an overcoat of only a binder resin) is provided on a microcapsule layer (10).

A glass plate or a resin plate (or a film, a sheet) is used for atransparent substrate (1). For example, soda-lime glass, low-alkaliborosilicate glass or alkali-free alumino-borosilicate glass can be usedas the glass plate, For example, polyethylene terephthalate (PET),polycarbonate, polyimide, polyethylenenaphthalate, polyethersulfone,acrylic resin or polyvinyl chloride can be used as the resin plate (or afilm, a sheet).

In a color electrophoresis type display medium panel of the presentinvention, a shape of a pattern of a color filter layer is notespecially limited and a preferred shape can be appropriately used. Forexample, a filter segment of a fine stripe shape in which the segmentsare parallel to each other or intersect with each other can be used.Alternatively, a filter segment in which the filter segments arearranged in a matrix in a plane can be used. For example, a pixelstructure in which R, G, B and W are combined as shown in FIG. 5 isfrequently used. However, a pixel structure is not limited to this. In acolor filter layer (2) used in the present invention, a plurality ofcolored patterns are arranged, and colored pixels are arranged inrespective pixel regions. A colored pixel colors transmission light forevery pixel. Generally, colored pixels of red (R), green (G) and blue(B) which correspond to light's three primary colors or of yellow (Y),magenta (M) and cyan (C) of three primary colors are arranged. Inaddition, here, W is a transparent resin used for a photo spacer or thelike. W is used with colored pixels so that brightness can be improvedby utilizing larger rays of reflection light. A black matrix is notusually used for a color filter comprising a multi color display panelof the present invention.

In a color electrophoresis type display medium panel of the presentinvention, the shape of a cross section of a color filter layer (2) is,as shown in FIG. 4, adjusted to become a certain shape in view ofapplicability of a microcapsule ink and image display characteristics. Afilm thickness of a color filter layer is 0.5-2.0 μm, more preferably0.7-1.3 μm. In a multi color display panel of the present invention,light passes twice through a color filter layer. Therefore, in order tomaintain brightness, a color resin having color characteristics withhigh transmittance is used. In the case of a film thickness of less than0.5 μm, necessary color density can not be balanced with adhesiveproperties to a transparent substrate. In addition, in the case of afilm thickness of more than 2.0 μm, fluctuation of the film thicknessdue to development or the like can not be controlled.

A step (difference in film thickness) between pixels inside a displayscreen or inside a pixel is equal to or less than 0.3 μm, and morepreferable 0.1 μm. In the case where the step is more than 0.3 μm, adifference in color density is recognized. In addition, an applicationsurface of a microcapsule ink becomes non-uniform such as a wave andtherefore image display may be influenced. This difference in filmthickness can be controlled by a composition of a resist ink, anexposure condition, a development condition or the like.

In addition, in a color filter for a liquid crystal display panel usinga back light, a black matrix (BM) is used between respective pixelpatterns for raising contrast and preventing a color mixture. Inaddition, in the case where BM is not used, in order to prevent leaklight, pixels which are adjacent to each other are overlapped.Therefore, an edge of a pixel rises. In the case where its height ismore than 0.3 μm, deviation of a microcapsule ink is generated. Thisinfluences uniformity on the application surface. Then, in a colorfilter of the present invention, pixels are not overlapped with eachother. As shown in FIG. 4, a final cross section shape of respectivepixels is usually a trapezoid. Respective pixels which are adjacent toeach other are not overlapped with each other while edges of the bottomsof the trapezoid contact with each other or are separately arranged.Further, a top edge of respective pixels of the trapezoid is within 5.0μm from a border of a pixel, and more preferably 3.5 μm from a border ofa pixel. In the case of a pixel having such a cross section shape,application is possible while a pixel does not rise and deviation of amicrocapsule ink is not generated. At the same time, non-uniformity ofan image as a surface wave can be controlled, utilization efficiency ofreflection light is high and a display panel having a high level ofbrightness can be obtained.

This color filter layer is generally manufactured as follows. A coloredlight sensitive resin or a transparent light sensitive resin, thecolored light sensitive resin being a light sensitive resin in which acolor agent of a pigment or a dye is dispersed or mixed, is applied to aglass substrate by a spin coating method or a spinless coating method soas to have a uniform thickness. Any excess solvent is dried and removed(photolithography). Thereafter, this resist film is irradiated with anactive energy beam using an ultrahigh pressure mercury lamp by aproximity exposure through a photo mask of a desirable shape. Thereby, acuring level (a negative type) or alkali solubility (a positive type) isincreased. Parts which can be dissolved by an alkali solution or thelike are removed, thereby development is performed. Further, post-bakingis performed. These operations are repeated several times as needed. Inaddition, the present invention is not especially limited to the abovemanufacturing method.

Then, according to necessity, the surface of the color filter layer (2)is polished and flattened. Thereafter, a transparent electrode layer (4)is formed. For example, a transparent conductive oxide of indium oxidesystem, tin oxide system, zinc oxide system such as ITO can be used as amaterial of the transparent electrode. A conventional technology such asvaporization method, sputtering method or CVD method can be used forforming this transparent electrode.

Hereinafter, a summary of the display principles of a color filter witha microcapsule which comprises a color electrophoresis type displaymedium panel of the present invention is explained.

As shown in FIG. 2, a pixel electrode (30) of a rear substrate (50) isconnected to a switching element (not illustrated) of each pixelelectrode. Thereby a positive and negative voltage can be appliedbetween a pixel electrode and a transparent layer (4). In order todisplay an image, usually, the pixel electrode (30) is connected to apower source of a circuit constitution of an active matrix driving type.When a voltage is applied to the pixel electrode (30), an electricalfield in the microcapsule layer (10) changes. When the pixel electrode(30) is a positive electrode, a negative charged particle in amicrocapsule (5) moves toward a side of the pixel electrode (30) of arear surface, and a positive charged particle moves towards a side ofthe transparent electrode layer (4) of a front surface. Similarly, whenthe pixel electrode (30) is a negative electrode, a positive chargedparticle moves towards a side of a pixel electrode, and a negativecharged particle moves towards a side of the transparent electrode layer(4). Here, if, for example, a black particle has a positive charge and awhite particle has a negative charge, the display color is the color ofa particle which moves towards a side of the transparent electrode layer(4) of a front surface. Therefore, light from an observer side isreflected by the particle, and the reflected light passes through acolor pattern of an opposing color filter, thereby the color of adesirable character or image can be displayed.

Next, a material and a component used for a color electrophoresis typedisplay medium panel of the present invention are further explained.

The microcapsule (5) used for forming a microcapsule with a color filteris comprised of a colored particle (6), a while particle (7), atransparent dispersion medium (8) and a microcapsule shell (9).

Generally, a microcapsule used for a microcapsule type electrophoresisdisplay panel is refined by a bolting method, a gravity separationmethod or the like. Its average diameter is 30-100 μm. Furthermore, theproportion of a microcapsule having a capsule with a diameter within 10μm with respect to an average diameter of a microcapsule is more than50%.

In an electrophoresis type display medium of the present invention, asshown in FIG. 3( a), definition is as follows. X is an average particlediameter 1 in any direction in the case where a particle diameter of amicrocapsule in a microcapsule layer is observed from a viewer side. Yis an average particle diameter 2 in a perpendicular direction. As oneexample thereof as shown in FIG. 3( b), the distribution of the particlediameter is adjusted as follows: when X=35-45 μm, the proportion ofmicrocapsules when the particle diameter of the microcapsule is equal toor more than X1 (=X−20 μm) and equal to or less than X2 (=X+20 μm), isequal to or more than 80%, and the proportion of microcapsules when theparticle diameter of the microcapsule is less than X1, is less than 20%,and the proportion of microcapsules when the particle diameter of themicrocapsule is more than X2, is less than 5%. When Y=35-45 μm, theproportion of microcapsules when the particle diameter of themicrocapsule is equal to or more than Y1 (=Y−20 μm) and equal to or lessthan Y2 (=Y+20 μm), is equal to or more than 80%, the proportion ofmicrocapsules when the particle diameter of the microcapsule is lessthan Y1, is less than 20%, and the proportion of microcapsules when theparticle diameter of the microcapsule is more than Y2, is less than 3%.The above distribution of particle diameter is a distribution in thecase where a panel is observed form a viewer side. A microcapsule in amicrocapsule layer observed from a horizontal direction has a shape inwhich the size in a vertical direction thereof is a little short.

A water type solvent such as alcohol is used for a microcapsuledispersion liquid. If there is no particular problem then water is used.

A transparent dispersion medium (8) is selected from an insulatingliquid in which an electrically charged particle can be properly andstably electrically charged, that is, an organic solvent which issubstantially insoluble in water. For example, long chain alcohol-basedsolvents such as dodecanol and undecanol; multicarbon ketones such asdibutyl ketone and methyl isobutyl ketone; aliphatic hydrocarbons suchas pentane, hexane and octane; alicyclic hydrocarbons such ascyclohexane and methylcyclohexane; aromatic hydrocarbons such asbenzene, toluene, xylene, hexylbenzene, butylbenzene, octylbenzene,nonylbenzene, decylbenzene, undecylbenzene, dodecylbenzene,tridecylbenzene, tetradecylbenzene and other benzenes having a longchain alkyl group; halogenated hydrocarbons such as methylene chloride,chloroform, carbon tetrachloride and 1,2-dichloroethane; and variousoils such as silicon oil and olive oil, or a mixture thereof areexemplified.

A black pigment such as aniline black and carbon black, a fine powdersuch as glass and resin, and a composite body thereof are used for ablack electrophoresis particle as a colored particle (6). In addition, ablack particle using carbon black is usually used in a multi colordisplay panel of the present invention which displays a multi color by acolor filter, In addition, a white inorganic pigment such as well-knowntitanium oxide, silica, alumina and zinc oxide, an organic compound suchas vinyl acetate emulsion, and a composite body thereof are used for awhite electrophoresis particle as a white particle (7).

According to necessity, a surface of the colored particle (6) and thewhite particle (7) is treated by using various surfactant agents,dispersing agents, organic compounds, inorganic compounds, metals or thelike. Thereby, the surface can have a surface electrical charge, anddispersing stability in a transparent dispersion medium (8) can beimproved.

A dispersion liquid A in which the colored particle (6) and the whiteparticle (7) are dispersed in a transparent dispersion medium (8) isenclosed in a microcapsule using a well-known method such as a phaseseparation method of a complex coacervation, an interfacialpolymerization method, an in-situ method and a hotmeltmicroencapsulation method. A microcapsule shell (9) is, for example, afilm of rubber or gelatin, the film having elastic property andflexibility so that the film can be subjected to necessary deformation.A material through which light transmits well is preferable for amaterial for forming a microcapsule. For example, urea-formaldehyderesin, melamine-formaldehyde resin, polyester resin, polyurethane resin,polyethylene resin, polystyrene, polyamide resin, acrylic acid esterresin, methacrylic acid ester resin, polyvinyl acetate resin, rubber andgelatine are exemplified. A single material thereof or a mixed materialthereof can be used.

A microcapsule ink is prepared by mixing a microcapsule dispersionliquid with a viscosity improver, surfactant agent, a binder resin (11)or the like, the microcapsule dispersion liquid having a dispersedmicrocapsule having an adjusted diameter distribution. A dielectricresin such as polylactic acid, phenol resin, polypropylene resin,acrylic resin, and polyurethane resin is used for a binder resin (11) ofa microcapsule ink.

The microcapsule layer (10) is formed as follows. The microcapsule inkis, as mentioned above, directly applied to the transparent electrodelayer (4) of a transparent substrate made of a glass substrate or aresin substrate on which the color filter layer (2) and the transparentlayer (4) are formed in advance. Application is performed by anapplication apparatus such as a screen printing type, a micro gravurecoater, a kiss coater, a comma coater, a die coater, a bar coater and acurtain coater. However, in the present invention, a slot die coater canbe preferably used.

As mentioned above, in general, the manufactured microcapsule layer (10)has a surface with bumps. Therefore, a distance between electrodessandwiching a microcapsule cell does not easily become constant.Therefore, it is preferred that a surface flattening layer is formed byapplying a surface flattening ink to the microcapsule layer (10). When asurface flattening layer is formed, an adhesive can be directly appliedto the surface flattening layer. In the case where an adhesive isdirectly applied without a flattening layer, if a non-applied spotexists such as a pin hole in the microcapsule layer (10), an adhesivedirectly contacts with the transparent electrode layer (4) in a side ofa color filter, thereby a dielectric constant changes. Therefore, it isdifficult for a voltage to be applied to a microcapsule. As a result,display becomes unclear.

In the surface flattening ink, a resin as a binder is dispersed in asolvent. It is preferable that a binder component thereof has adielectric constant which is equal to a dielectric constant of a resinof a binder component used for a microcapsule ink or a binder componentused for an adhesive. It is most preferable that binder resin componentsof a microcapsule ink, an adhesive layer and a surface flattening inkare identical. If resins having different dielectric constants are used,resins having different constants are arranged between electrodes.Further, thicknesses of respective resins differ according to a size ofa microcapsule at this part. In this case, a voltage applied to amicrocapsule does not easily become uniform over the entire region of ascreen.

A solvent used for a microcapsule ink can be used for a solvent of asurface flattening ink. However, a water system solvent such as alcoholmay be also used. Application of a surface flattening ink is performedby using an application apparatus such as a curtain coater and a slotdie coater. An application type which cuts an application liquid, forexample a blade coater, can not be used because it breaks themicrocapsule inside the microcapsule layer.

It is preferable that a thickness of the surface flattening layer is10-30 μm. In the case where the thickness is lower than 10 μm, bumps ofa surface of the microcapsule can not be flattened. On the other hand,in the case where the thickness is more than 30 μm, a distance betweenelectrodes becomes long. This causes an increase in the driving voltage.

As mentioned above, a surface flattening layer is formed and a solventis sufficiently vaporized. Thereby, a color filter with a microcapsuleis formed. This color filter with a microcapsule is attached to a rearelectrode plate in which a pixel electrode is arranged on a rearsubstrate, through an adhesive layer, while position adjustment betweena colored pattern (a pixel) of a color filter and a pixel electrode of arear electrode is performed. Thereby, a color electrophoresis typedisplay medium panel can be manufactured.

It is preferable that a synthetic resin type adhesive such as anurethane resin type adhesive and an acrylic resin type adhesive is used.Especially, an adhesive using a resin having a high dielectric constantis preferable.

It is possible to directly apply an adhesive to the microcapsule layeror the pixel electrode. However, in the manufacturing method of thepresent invention, an adhesive using the same component as a binderresin used for the microcapsule ink is applied to a resin peelingsubstrate in which a conductive layer is formed between a silicon filmand a resin substrate. A resin peeling substrate with an adhesive ispreferably used as an adhesive sheet. When an adhesive having acomponent which is the same as a binder resin used for a microcapsuleink is used, an affinity with the interface of a resin is increased andthereby peeling does not easily occur. In addition, dielectric constantsare similar to each other and therefore a voltage applied to anmicrocapsule becomes uniform over the entire surface.

In addition, if a resin peeling substrate in which a conductive layer isformed between a silicon film and a resin substrate is used, thefollowing merit is obtained. A multi layer substrate in which theadhesive sheet is formed on a color filter with a microcapsule, aso-called color filter electrophoresis display type front plate can besubjected to a driving evaluation and quality confirmation. In addition,a conductive layer used here does not have to be transparent and thefollowing films may be used. A thin film on which a metal such as copperand aluminum is deposited or electrodeposited; and a film to which aconductive polymer is applied can be used.

In a microcapsule type electrophoresis type display medium panel, in thecase where a large proportion of a surface (that is, a reflectionsurface) of a microcapsule closely contacts a side of a transparentelectrode layer in a viewer side, brightness and image quality areimproved. In a color electrophoresis type display medium panel of thepresent invention, a microcapsule layer is directly formed on atransparent electrode layer on a highly flat color filter layer.Therefore, a microcapsule ink is easily and uniformly applied. Inaddition, a microcapsule layer is very near a color filter layer, whichis a surface of a display. Thereby, a multi color display panel withimproved image quality can be obtained. In addition, a multi colordisplay panel with small non-uniformity of color density can beobtained, the small non-uniformity of color density caused by adifference in a film thickness of a color filter layer through whichlight transmits twice (a reflection type).

In addition, in a color electrophoresis type display medium panel of thepresent invention, a particle diameter of a microcapsule in amicrocapsule layer is adjusted to have a distribution of the abovespecific range. Thereby, applicability of a microcapsule ink is good,and a uniform application film is obtained. Further, in a state where amicrocapsule is floated inside a binder resin or in a state where amicrocapsule is deposited to a side of an adhesive layer, a proportionof the microcapsules located at a position far from a transparentelectrode layer is small, and a proportion of microcapsules in which areflection surface closely contacts a side of a transparent electrodelayer of a viewer side is large. Therefore, in addition to the abovementioned flatness of a color filter, non-uniformity inside a displayscreen and respective pixels does not exist, reflectance is high,brightness is improved, and excellent color display becomes possible.

In addition, in a color electrophoresis type display medium panel of thepresent invention, a thickness of a microcapsule layer is equal to orless than an average particle diameter X or an average particle diameterY, and is equal to or more than 0.8×X1 or 0.8×Y1. That is, a largemicrocapsule is slightly shortened in a thickness direction by pressure,thereby neighboring microcapsules closely contact with each other. Inaddition, small microcapsules rarely overlap with each other. Inaddition, the distance by which the microcapsule moves becomes uniform.Thereby, properties of a microcapsule in driving and response accordingto a change of an electrical field by applying a voltage are excellent,and display characteristics are improved.

In addition, if the present invention is compared with a conventionaldisplay panel which is formed by attaching a microcapsule layer to acolor filter substrate which is separately manufactured, an unnecessarylayer such as adhesive is not arranged between a microcapsule layer anda color filter layer in a structure of the present invention. Therefore,light reflected by a microcapsule layer passes a minimum layer andthereby a display brightness is improved compared with the conventionaldisplay panel. In addition, if a color filter layer is separated from amicrocapsule layer, a color deviation between a display of amicrocapsule layer and a color filter is observed. If a color filterlayer is closely-attached to a microcapsule, the disparity is notobserved, thereby narrowing of a viewing angle does not occur.

EXAMPLE

Hereinafter, specific examples of the present invention are explained.

Example 1

A titanium oxide powder (a white powder) of 3 μm average diameter, thesurface of which was covered by a polyethylene resin, and a carbon blackpowder (a black powder) of 4 μm average diameter, the surfaces of whichare treated by alkyl trimethylammonium chloride, were dispersed in atransparent dispersion medium of tetrachloroethylene. Thereby adispersion liquid A was prepared. In this case, a white particle wascharged negative, and a black particle was charged positive.

Next, a water solution in which gelatin and sodium polystyrene sulfonatewere dissolved in water was prepared. The water solution was mixed withthe dispersion liquid A. The mixed liquid was adjusted to 40 degreesCelsius. Thereafter, while the temperature of the mixed liquid wasmaintained, the mixed liquid was stirred by a homogenizer. Thereby anO/W emulsion was obtained.

Next, the O/W emulsion and a water solution in which gum arabic wasdissolved in water were mixed by a dispenser at 40 degrees Celsius.While the temperature of the solution was maintained at 40 degreeCelsius, the pH of the solution was adjusted to 4 using acetic acid. Amicrocapsule having a gelatin/acacia shell material was formed by acomplex coacervation method.

Further, the temperature of the solution was reduced to 5 degreeCelsius. Thereafter, a formalin solution (37 wt %) was added and therebya wall material of a microcapsule shell was hardened. Thereby, amicrocapsule was obtained in which the dispersion liquid in which awhite particle (titanium oxide) and a black particle (a carbon blackparticle) were dispersed was enclosed.

The microcapsule obtained in this way was bolted and the particlediameter of the microcapsule was made uniform so that the averageparticle diameter was 40 μm, the particle diameter was 20 μm-60 μm, anda proportion of such microcapsules was 80%. Particle diameter was lessthan 20 μm, a proportion of such microcapsules was less than 20%.Particle diameter was more than 60 μm, and a proportion of suchmicrocapsules was less than 5%.

Next, a microcapsule with a uniform diameter was used as a solidcontent. A water dispersion liquid having 40 wt % of the solid contentwas prepared. A microcapsule ink was manufactured by mixing the waterdispersion liquid with an urethane system binder having 25 wt % of solidcontent (CP-7050, a product of DIC), a surfactant agent, a viscosityimprover, and a pure water.

On the other hand, a color filter was manufactured by the followingmethod. Here, “part” means “parts by weight”. Firstly, an acrylic resinwas manufactured by copolymerizing 50 parts of butyl methacrylate, 20parts of methyl methacrylate and 30 parts of acrylic acid whereincyclohexane was used as a solvent.

An acrylic resin solution was prepared using 25 parts of the acrylicresin and 47 parts of a solvent. 20 parts of red pigments (Pigment Red22) was mixed with the acrylic resin solution. This was dispersed for 1hour using a bead mill. Thereafter, further, 4 parts ofdipentaerythritol and 4 parts of hexaacrylate as a light sensitivemonomer, and 0.3 part of bis(2,4,6-trimethylbenzoyl)—phenyl phosphineoxide as a photopolymerization initiator were mixed by a disperser.Thereby, a red color photo resist material was prepared.

This red color photo resist material was applied to a transparent glasssubstrate (400 mm (vertical)×320 mm (horizontal), thickness 0.7 mm) by aspin coating method. The coated glass was left for 5 minutes at a roomtemperature and a film surface was flattened. Thereafter, the coatedglass was dried for 20 minutes at 70 degrees Celsius and a red colorphoto resist layer was formed.

Then, this red color photo resist layer was contact-exposed under acondition of an exposure amount of 150 mJ/cm² through a photo mask whichwas arranged at a position of red color exposure, using an ultrahighpressure mercury lamp. The photo mask had six patterns, with the size ofeach of the patterns being 97.28 mm (vertical)×128.08 mm (horizontal)corresponding to a display screen, as shown in FIG. 5( b). Further, asshown in FIG. 5( a), the photo mask corresponds to a pattern of a pixelsize of 302 μm×306 μm which was comprised of R, G, B and W. The patterncorresponding to a pixel was repeated in both a vertical direction and ahorizontal direction in the photo mask. As shown in FIG. 5( a), a subpixel size was 151 μm×153 μm. After the exposure, a spray development inwhich 1% of sodium carbonate solution was sprayed under 1 kg/cm² ofpressure was performed for 30 seconds and the non-exposed part wasremoved and a glass substrate was exposed. The glass substrate was driedafter the developing process. Thereafter, the glass substrate was heatedfor 1 hour at 230 degrees Celsius, a film hardening process wasperformed, and a red color patter of 1.1 μm film thickness was obtained.

Next, a green photo resist layer was formed on a glass substrate withthis red color pattern. Here, a green pigment (Pigment Green 7) was usedas a colorant, and a green photo resist material which was formed usingthe same composition as the red photo resist was used. Then, a photomask similar to the above photo mask was arranged at a position where agreen pattern was fowled. Then, a contact exposure was performed under acondition of 200 mJ/cm² (exposure amount). After the exposure, a spraydevelopment in which 1% of sodium carbonate solution was sprayed under 1kg/cm² of pressure was performed for 30 seconds, the non-exposed partwas removed and a glass substrate was exposed. Similarly, the glasssubstrate was dried after the developing process. Thereafter, the glasssubstrate was heated for 1 hour at 230 degrees Celsius, a film hardeningprocess was performed, and a green color pattern of 1.2 μm filmthickness was obtained.

Further, similarly, a blue photo resist material using a blue pigment(Pigment Blue 15:6) as a colorant was used, and a blue photo resistlayer was formed. Then, a photo mask similar to the above photo maskarranged at a position where a blue pattern was formed. A non-exposedpart was removed, and the glass substrate was exposed. Similarly, theglass substrate was dried after the developing process. Thereafter, theglass substrate was heated for 1 hour at 230 degrees Celsius, a filmhardening process was performed, and a blue color pattern of 1.1 μm filmthickness was obtained.

Next, a light sensitive acrylic resin from which only a color pigmentwas excluded was used. By performing similar processes, a W(transparent) pattern of 1.1 μm film thickness was obtained. Respectivesub pixels, R, G, B and W, had a difference in film thickness at most0.1 μm, and did not overlap with each other in the case where the subpixels are adjacent to each other. The sub pixels were arranged so thatan edge of the bottom of each of the sub pixels contacts with eachother. In the case where the edge did not contact with each other, thespace between the edges was equal to or less than 1.0 μm. In addition,in any part, a top edge was within 3.5 μm from a border of a pixel.

In this way, a substrate in which a color filter layer was formed on aglass substrate was obtained. Here, in the color filter layer, therewere six screens of 6 inches, each screen being 97.28 mm(vertical)×125.08 mm (horizontal), the size of a sub pixel being 151μm×153 μm, and the size of a pixel comprising R, G, B and W being 302μm×306 μm. Next, a transparent electrode layer of ITO of 150 nm filmthickness was deposited and formed on the entire surface of the colorfilter layer and the exposed glass substrate without polishing andproviding an over coat.

Next, the microcapsule ink was directly applied to the transparentelectrode layer on the transparent glass substrate with the color filterlayer, using a slot die coater. The application was performed asfollows. A thickness of a microcapsule layer was 40 μm. Microcapsulesdid not overlap with each other and a microcapsule with a large diameterwas pushed into the microcapsule layer. After application, it was driedfor 10 minutes at 60 degrees Celsius and a color filter with amicrocapsule was obtained.

Further, a surface flattening ink including urethane binder with 25% ofsolid content (CP-7050, a product of DIC) was applied to themicrocapsule layer of the color filter with the microcapsule layer usinga slot die coater. The ink was dried, and a color filter with amicrocapsule on which a surface flattening layer of 10 μm thickness wasarranged was obtained.

Separately, aluminum of 100 nm thickness was deposited on one surface ofa polyethylene terephthalate sheet of 50 μm thickness as a conductivelayer. Further, a silicon type peeling coat layer was arranged on thealuminum. A polyester-urethane system adhesive was applied to a side ofthe silicon type peeling coat layer to 20 μm and an adhesive sheet wasprepared.

Next, the adhesive sheet was attached to the color filter with themicrocapsule with the surface flattening layer and a color filterelectrophoresis display type front plate was obtained. The front platehad six screens with a display screen of 6 inches. In this state, avoltage was applied between the transparent electrode layer and theconductive layer, and a driving test of the microcapsule layer wasperformed.

Next, while the polyester-urethane system adhesive was left on the frontplate, the polyethylene terephthalate of 50 μm thickness with thesilicon type peeling coat was peeled from the front plate. Whileposition adjustment using a position determining mark of the colorfilter was performed, the front plate was attached to a surface of apixel electrode of a rear electrode plate with the pixel electrode ofITO which had a circuit constitution of an active matrix driving typeusing a thin film transistor on a glass (a TFT substrate correspondingto 6 inches six color filters), wherein 0.50 MP of pressure was appliedto the attachment. Further, six display screens were separated in to sixpieces. Thereby, a color electrophoresis type display medium panel ofthe present invention was obtained.

A voltage of about ±15 V was applied between the transparent electrodeof the front surface and the pixel electrode of the rear surface of therespective display panels of Example 1, using a standard voltage/currentgenerator (a product of Yokogawa Electric Corporation). Actual displayproperties were evaluated. In addition, reflectances in cases of colordisplay (white display) and black display were measured using a colordifference meter (CR-400, a product of Konica Minolta), thereby contrastwas evaluated. Here, contrast=reflectance in the case of a color display(white display)/reflectance in the case of a black display. Further,visual lightness L* was measured by using the meter.

As a result, the six display panels in Example 1 were very bright(reflectance of white was 23%), had an excellent contrast (12:1, thiswas almost the same as a mono color type) and a multi color displaycould be realized. Non-uniformity of an image or difference in colordensity between the six panels due to non-uniformity of application of amicrocapsule ink was not detected. Further, in all the display panels,color deviation between a front surface observation and a horizontaldirection observation was not detected. An excellent color display inwhich disparity of color depending on a viewing angle were also improvedwas possible as an electronic paper.

(The disclosure of Japanese Patent Application No. JP2009-217154, filedon Sep. 18, 2009, is incorporated herein by reference in its entirety.)

1. A color electrophoresis display medium panel, comprising: atransparent substrate; a color filter layer; a transparent electrodelayer; a microcapsule layer; an adhesive layer; and a rear electrodeplate, wherein the transparent substrate, the color filter layer, thetransparent electrode layer, the microcapsule layer, the adhesive layerand the rear electrode plate are arranged in that order, themicrocapsule layer is directly formed on the transparent electrodelayer, the microcapsule layer is comprised of a binder resin and amicrocapsule, the microcapsule being dispersed in the binder resin, adispersion liquid in which electrophoresis particles are dispersed in atransparent dispersion medium is enclosed in the microcapsule, and anoptical reflection property of the microcapsule changes by a change ofan electric field by an applied voltage, the rear electrode plate is anelectrode plate in which a pixel electrode is arranged on a substrate,and the microcapsule has the following distribution wherein an averageparticle diameter of the microcapsule in a direction observed from aviewer is defined as X, and an average particle diameter of themicrocapsule in another direction perpendicular to the directionobserved from a viewer is defined as Y, X=35-45 μm, a proportion of themicrocapsules when a particle diameter of the microcapsule is equal toor more than X1 (=X−20 μm) and a particle diameter of the microcapsuleis equal to or less than X2 (=X+20 μm), is equal to or more than 80%, aproportion of the microcapsules when a particle diameter of themicrocapsule is less than X1, is less than 20%, a proportion of themicrocapsules when a particle diameter of the microcapsule is more thanX2, is less than 5%, and, Y=35-45 μm, a proportion of the microcapsuleswhen a particle diameter of the microcapsule is equal to or more than Y1(=Y−20 μm) and a particle diameter of the microcapsule is equal to orless than Y2 (=Y+20 μm), is equal to or more than 80%, a proportion ofthe microcapsules when a particle diameter of the microcapsule is lessthan Y1, is less than 20%, a proportion of the microcapsules when aparticle diameter of the microcapsule is more than Y2, is less than 5%.2. The color electrophoresis display medium panel according to claim 1,wherein the electrophoresis particles are two kinds of particles havingdifferent surface electrical charges, one of the particles being acolored particle and the other being a white particle.
 3. The colorelectrophoresis display medium panel according to claim 1, wherein afilm thickness of the color filter layer is 0.5-2.0 μm, a step betweenpixels or inside a pixel inside a display screen, the step being thedifference of the film thickness, is equal to or less than 0.3 μm, oneof the pixel does not overlap with an adjacent pixel, and a top edge ofeach of the pixels of a trapezoid shape is within 5.0 μm from a borderof the pixel.
 4. The color electrophoresis display medium panelaccording to claim 1, wherein, in a state where the microcapsule layeris observed from a direction of a cross section of the panel, athickness of the microcapsule layer is equal to or less than X or Y, andis equal to or more than 0.8×X1 or 0.8×Y1.